Isolation, identification and biotyping of virulent Yersinia enterocolitica from pasteurized milk
Subject Areas :
Food Science and Technology
شهرام Hanifian
1
1 - Department of Food Science and Technology, Faculty of Agriculture Science, Tabriz Branch, Islamic Azad University, Tabriz, Iran.
Received: 2012-06-10
Accepted : 2012-06-26
Published : 2012-02-20
Keywords:
PCR,
Pasteurized Milk,
Ail,
VirF,
Y. enterocolitica,
Abstract :
In order to investigate the presence of virulent Yersinia enterocolitica in pasteurized milk, 242 samples were collected from Tabriz retails from 2011 to 2012. The samples were enriched in PSBB. Afterwards, virF and ail genes were exploited as target sequences for the detection of virulent Y. enterocolitica. PCR-positive samples were cultured on CIN agar and MacConkey agar. The selected isolates were confirmed by second-phase duplex PCR. For the biotyping of Y. enterocolitica, certain biochemical tests were performed on the isolate. The pasteurized milk samples were further analyzed for the enumeration of hygiene indicator bacteria and qualitative alkaline phosphatase (ALP) test. Virulent Y. enterocolitica were detected in 6.61% (16/242) of samples by ail-PCR, however, using virF-PCR 4.13% (10/242) of the samples were identified as positive. Among PCR-positive samples only 0.41% (1/242) were isolated by culture method and confirmed by second-phase duplex-PCR. Based on the biochemical assays, the isolated Y. enterocolitica was identified as biotype 4. Furthermore, 11.57% (28/242) of the samples were found positive for alkaline phosphatase test. The results revealed that the number of hygiene indicator bacteria in ALP-positive samples was significantly (p<0.01) higher than ALP-negative samples. Since Y. enterocolitica is very susceptible to pasteurization process, cross contamination could be the main reason for the presence of virulent Y. enterocolitica in the pasteurized milk.
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